It has been conventional to drive accessory components associated with internal combustion engines and the like, such as used in vehicles, by means of flexible power transmission belts. A common form of such power transmission belt comprises a V-belt entrained about complementary grooved pulleys on the engine and accessory equipment.
In the modern vehicle engine, a number of such accessories, such as alternators, cooling fans, power steering pumps, air conditioner compressors, etc., are provided. It has been conventional to utilize a plurality of individual V-belts for driving such a plurality of accessories.
More recently, multiple ribbed V-belts have been developed wherein the inner surface of the belt is provided with a plurality of side-by-side longitudinally extending V-shaped ribs. Such a belt has been utilized to drive a plurality of the accessories by directing the multiple ribbed belt in a serpentine path wherein the V-ribbed portion engages, successively, the pulleys of the different accessories.
The back surface of the belt is engaged with an idler pulley for regulating the tension of the belt and, in certain instances, the back surface is used to drive a flat pulley. Such drive systems have not proven completely satisfactory in that the back surface tends to wear, thereby causing slippage relative to the driven pulley.
It has been proposed to overcome the problem of the back surface slippage by providing, on the back surface, a plurality of ribs similar to the plurality of ribs on the front surface, whereby both surfaces may drive multiple grooved pulleys in the same manner. One such double V-ribbed belt is disclosed in U.S. Pat. No. 2,728,239.
It has been found that such double V-ribbed belts are limited in their useful life because of cracking of the ribs after a relatively small number of hours of power transmission operation. The belts having a flat outer surface are limited in the useful life thereof because of substantial slippage under load.